// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

using System.Threading;
using Markdig.Syntax;

namespace Markdown.VT;

/// <summary>
/// Renderer for adding VT100 escape sequences for items in a list block.
/// </summary>
internal class ListItemBlockRenderer : VTObjectRenderer<ListItemBlock>
{
    protected override void Write(VTRenderer renderer, ListItemBlock obj)
    {
        if (obj.Parent is ListBlock parent)
        {
            if (!parent.IsOrdered)
            {
                foreach (var line in obj)
                {
                    RenderWithIndent(renderer, line, parent.BulletType, 0);
                }
            }
        }
    }

    private static void RenderWithIndent(VTRenderer renderer, MarkdownObject block, char listBullet, int indentLevel)
    {
        // Indent left by 2 for each level on list.
        string indent = Padding(indentLevel * 2);

        if (block is ParagraphBlock paragraphBlock)
        {
            renderer.Write(indent).Write(listBullet).Write(" ").Write(paragraphBlock.Inline);
        }
        else
        {
            // If there is a sublist, the block is a ListBlock instead of ParagraphBlock.
            if (block is ListBlock subList)
            {
                foreach (var subListItem in subList)
                {
                    if (subListItem is ListItemBlock subListItemBlock)
                    {
                        foreach (var line in subListItemBlock)
                        {
                            // Increment indent level for sub list.
                            RenderWithIndent(renderer, line, listBullet, indentLevel + 1);
                        }
                    }
                }
            }
        }
    }

    // Typical padding is at most a screen's width, any more than that and we won't bother caching.
    private const int IndentCacheMax = 120;

    private static readonly string[] IndentCache = new string[IndentCacheMax];

    internal static string Padding(int countOfSpaces)
    {
        if (countOfSpaces >= IndentCacheMax)
        {
            return new string(' ', countOfSpaces);
        }

        var result = IndentCache[countOfSpaces];

        if (result == null)
        {
            Interlocked.CompareExchange(ref IndentCache[countOfSpaces], new string(' ', countOfSpaces), comparand: null);
            result = IndentCache[countOfSpaces];
        }

        return result;
    }
}
